We had four fish in our tank, then - after a few months - added two more. One by one they all died off (except a snail, he survived). So, my husband went out and bought several new fish. He cleaned the tank thoroughly, then added the new fish. We've only had them for about two weeks, and almost all of them have died. I started noticing little white spots on the fish just a day or two before they die and they swim around a bit funny, almost like they're drunk. They swim sideways or just float to the bottom before swimming straight up again. We had Stress Coat, which we had added when we got the new fish, but someone told us that he believed the Stress Coat actually made matters worse. We don't really know much about caring for fish, but would like to figure this out. Any suggestions for 'fixing' the environment??